Pressure control device



y 1953 J. A. DRAKE 2345240 PRESSURE CONTROL DEVICE 1 Filed Oct. 11, 1948 INVEN TOR.

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Armin 5x5 Patented July 14, 1953 2,645,240 PRESSURE CONTROL DEVICE John A. Drake, Los .Angeles, Calif assignor to Marquardt Aircraft Company, Van Nuys, Calif., a corporation of California Application October 11, 1948, Serial No. 53,792

exercise a control over two critical pressures and to maintain these pressures in a predetermined ratio. This can be accomplished by means of a flexible diaphragm, by exposing a part of one side of the diaphragm to a vacuum and applyin the pressures which it is desired to control the unequal areas on opposite sides of the diaphragm. Mathematically stated, if P1 and P2 are the pressures which it is desired to regulate, and if the diaphragm areas to which these pressures are applied are S1 and S2, respectively, then the net force acting upon the diaphragm is nil if the pressures are such that the Equation 1 [or s q ivalent (1=a)l is satisfied.

l I QSE P s (1a) It is apparent that, by appropriately selecting the values of S1 and S2, and by connecting the diaphragm with a valve or other means of controlling one or the other of the pressures, it is possible to provide continuous, automatic control of the pressures, so as to maintain P1/P2 at a selected value.

Such means, however, is difficult to adjust to satisfy a different set of conditions. Thus, if it is desired to maintain the ratio P1/P2 at a different value, it is necessary to vary the value of S2 or S1. Mechanical means of accomplishing this are possible, but are awkward and difiicult to manipulate and not too accurate in'their performance.

It is an object of the present invention to provide an improved pressure control method and apparatus.

It is a further object of the invention to provide a device and a method of controlling the ratio of two gas pressures or, stated in other words, to multiply a given gas pressure, such device being readily adjustable by pneumatic means to vary the pressure ratio without resort to mechanical means for varying S1 and S2.

These and other object 01' the invention will be apparent from the ensuing description and the appended claims.

6 Claims. (01. 137-100) 2 One form which the invention may assume is exemplified in the following description and illustrated by way of example in the accompanying drawing, in which the single figure is a diagrammatic representation of the control device of the invention as applied to actuate a valve which, in turn, controls one of the pressures.

Referring now to the drawing, the pressure control or pressure multiplying device comprises a gas-tight chamber l0, and disposed within such chamber is a flexible diaphragm II and on one side thereof is provided a bellows l2. The bellows I2 divides the space to the left of the diaphragm into a central space or chamber 13 and an annular space H, the latter space being maintained under high vacuum. The diaphragm area exposed to the central chamber i3 is designated as S1, andthe opposite diaphragm area as S2..

An inlet duct I5 is provided, opening into the right-hand chamber N5 of the device and inlet and outlet conduits and I8, respectively, are provided for thecentral chamber [3 in the lefthand'portion of the device. The inlet duct I! is provided with a convergent-divergent or'choked section l9, having a throat S and the outlet duct is provided with a similar convergent-divergent or, choked section 20, having a throat Sr, this latter throat being variable by means of a needle valve' 2l' having a pointer 22 and, associated therewith, a scale 23, which may be calibrated for a purpose explained hereinafter; As also illus trated, a rod or valve stem 30 is secured at one end to the diaphragm H and at its other end to a valve 3! disposed in a duct 32, which, for purposesof illustration, is indicated as a fuel duct.

In operation, the pressure control device functions as follows: The gases which it is desired to control are admitted to the ducts l5 and I1 and, of course, that admitted to the central chamber l3 through the duct I1 is vented through the outlet duct [8. Gas entering through the duct l5 and having a pressure P2 exerts upon the righthand side of diaphragm l I a force equal to P2 S2. The force exerted on the left-hand side of the diaphragm is determined not only by the gas pressure P1 and the diaphragm area Si, but also by the throat areas S3 and S4 of the choked sections l9 and 2D. This force may be regarded as the product of anefiective pressure P3 in the chamber I3 and the areasi; i. e., P3.S1.

I have dis'covered'that a simple, linear relation exists between the effective pressure P3 and the variable throat area S4. Such relation exists when the inlet and outlet orifices are choked, and the entrant pressure P1 is sufliciently high that 3 sonic velocity is achieved in the throats S3 and s4. Derivation of this linear relation follows:

The following mass flow parameter for the flow of a compressible fluid through an orifice can be derived from the basic laws of fluid mechanics:

q j x/ P,S R v+ y-2 l ]2 -1) The terms used in this equation have the following meaning:

Provided the pressure is sufficiently high, the Mach number M at the throat of an orifice of the type illustrated in the drawing will be equal to 1. Further, the quantities y, R and Tt may be regarded as constants. It thus follows from Equation 2 that the mass flow parameter can be simplified as follows:

( ITHS= where C is a constant.

In the system described in the drawing, m1=m2. Hence, from Equation 3,

Inasmuch asSa is constant and only S4 is varied, this equation reduces even further to the proportionality:

It is thus apparent that, with a simple device such as illustrated in the drawing, and merely by manipulation of the needle valve 2|, it is possible to vary the outlet orifice S4 andthereby vary the effective pressure P3 in chamber I3. It'is also apparent that the scale 23, which is scanned by the pointer 22, can be readily calibrated so as to indicate different values of Pl/P2. Merely by moving the needle valve 2| so as to locate the pointer opposite the desired value of Pl/PZ on the calibrated scale, the actual pressure P1 is multiplied by a factor to provide a, different effective pressure P3 and thus to maintain a different value of Pl/P2. Applications of this device will be readily apparent. Thus the needle valve 2| may be operated manually, and when set at a given value of Pl/PZ, the apparatus will function automatically to control the valve 3| so as to increase or decrease flow of fuel to an engine, so as to maintain the desired pressure ratio. Alternatively, the needle valve 2| may be actuated automatically by a force exerted directly or indirectly by the system under control.

A practical application of the device and method of this invention is described in my co-pending application Serial No. 53,791, filed October 11, 1948, entitled "Temperature Control System, to which reference may be had for complete details. In the said application there is described a system for controlling the turbine inlet temperature of a turbojet engine, in which the fuel line is provided with a valve actuated by 2. flexible diaphragm as described above and as shown in the drawing. In such system it is desired to exert a force on one side of the diaphragm which is proportional to a temperature and to a pressure prevailing in theengine. "This. is accomplished by admitting the gas to one side of the diaphragm through a choked duct and venting it through a choked duct similar to the choked ducts l9 and 20 described above. The outlet duct is controlled by a needle valve whose travel is determined by a thermal expansive diaphragm which is subjected-to the process temperature under consideration.

Many other applications of the pressure control device herein described will be apparent to one skilled in the art, and it will also be apparent that either the inlet or the outlet orifice may be controlled, as desired, and that the net force on the diaphragm may be used to operate a valve in a fuelline or for any other purpose.

It is thus apparentthat apressure control device and a pressure control methodare provided which are operable to control a pressure, or to control the ratio between two pressures, andto vary such ratio as desired automatically and without any mechanical change in the system other than movement of a simple valve.

While I have shown the preferred form of my invention, it is to be understood thatvarious changes may be made in its construction by those skilled in the art without departing from the spirit of the invention as defined in the appended claims.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. A pressure control device comprising a chamber, a pressure responsive member disposed therein presenting opposite sides of areas S1 and S2,

means for introducing gas to one side of area Si, means for introducing gas to the other side of area S2, and means for varying the effective gas pressure exerted on area S1, said means comprising an inlet duct having a convergent-divergent section, an outlet duct having a convergent-divergent section and a valve operable to vary the throat area of one of said sections.

2. A pressure control device comprising a chamber, a diaphragm disposed therein,.a duct for ad-' mitting gas to one side of said diaphragm, and a gas inlet and a gas outlet for admitting a gas to the opposite side of said diaphragm and venting the gas therefrom, said inlet and outlet being each provided with a convergent-divergent section, and a valve for one of said sections operable to vary the throat area thereof.

3. A pressure control device comprising a cham ber, a diaphragm disposed therein, a duct for admitting gas to one side of said diaphragm, and a gas inlet and a gas outlet for admitting a gas to the opposite side of said diaphragm and venting the gas therefrom, said inlet and outlet being each provided with a convergent-divergent section, and a valve for said outlet operable to vary the throat area of the convergent-divergent section thereof.

4. A pressure control device comprising a chamber, a diaphragm disposed therein, a bellows disposed on one, side of and secured to said diaphragm, said bellows defining a central area and an annular evacuated area, a duct for admitting a gas to the opposite side of said diaphragm, inlet and outlet ducts for'said bellows, a convergentdivergent section disposed in each of said inlet and outlet ducts, and a valve operable to vary the throat area of one of said sections.

5. A control device comprising a chamber, a pressure-responsive diaphragm mounted within said chamber, means for supplying fluid under pressure to each side of said diaphragm,'means for limiting the eifective area of one side of said diaphragm, said means including a flexible partition dividing the space of one side of the bellows into a plurality of sub-chambers, the means for supplying fluid under pressure to one of said subchambers comprising a choked inlet and a choked outlet, and. valve means for varying the area of the choked outlet. V

6. A pressure control device comprising a chamher, a pressure-responsive diaphragm mounted in said chamber anddividing said chamber into a pair of sub-chambers, means for supplying fluid under pressure to one side of said diaphragm, means for limiting the effective pressure-responsive area of the other side of said diaphragm, said means including an annular bellows, means for admitting fluid under pressure to said bellows ineluding a choked inlet and means for permitting egress of fluid from said bellows comprising a choked outlet and a valve for varying the effective area of said choked outlet, and valve means actuated by the movement of said bellows.

JOHN A. DRAKE.

References Cited in the file of this patent UNITED STATES PATENTS 

